paralelling technique

PARALLELING TECHNIQUE

Definition and Synonyms

  • Paralleling Technique: Also known as the Extension Cone Paralleling Technique (XCP), Right-Angle Technique, or Long-Cone Technique.

  • A method used to expose periapical films.

Basic Terminology

  • Parallel: Lines moving/lying in the same plane, separated by the same distance, and never intersecting.

  • Intersecting: To cut across or through.

  • Right Angle: 90 degrees formed by two lines perpendicular to each other.

  • Perpendicular: Intersecting at or forming a right angle.

  • Long Axis of a Tooth: An imaginary line dividing the tooth longitudinally into two equal halves.

  • Central Ray: The central portion of the primary beam of x-radiation.

Basic Principles of the Paralleling Technique

  1. Place the film in the mouth parallel to the long axis of the tooth being radiographed.

  2. Direct the central ray of the beam perpendicular to the film and long axis of the tooth.

  3. Use a film holder to keep the film parallel with the long axis of the tooth.

Achieving Parallelism

  • Film must be placed away from the tooth towards the midline of the oral cavity to achieve parallelism.

  • Object-Film Distance (OFD) must be increased to keep the film parallel due to the curvature of the palate.

  • A long cone (16” cone) is utilized, resulting in decreased image magnification and improved definition.

XCP Holders

  • Understand the components of XCP holders and their use in different areas of the mouth.

Film Selection

  • Assessment of the oral cavity is necessary to determine appropriate film size based on anatomical considerations (palate, torus, floor of mouth).

  • Anterior Periapicals: Use No. 1 or 2 film for adults, No. 1 film for children. Long portion should be vertical.

  • Posterior Periapicals: Use No. 2 film for adults, No. 1 film for children. Long portion should be horizontal.

General Rules for Film Placement

  • Cover the prescribed area to be examined.

  • Film must be parallel to the tooth's long axis and positioned away towards the midline.

  • Central ray must be directed perpendicular to the film.

  • Central ray of the x-ray beam should be directed through the contact areas between the teeth.

  • Ensure the x-ray beam is centered on the film to avoid “cone cut” errors.

Client Preparation for the Paralleling Technique

  1. Inform the client about the procedure.

  2. Prepare the required films and film holders.

  3. Adjust the chair to an upright position suitable for the radiographer.

  4. Align the client’s head to ensure the maxillary arch is parallel to the floor.

  5. Shield the client with a lead apron and thyroid collar.

  6. Remove any superimposed objects before proceeding.

Exposure Sequence

  • Begin with the maxillary right canine for anterior films, progressing to maxillary left canine. Then switch to mandibular left canine and finish at mandibular right canine.

  • If using size 2 film, 3 maxillary and 3 mandibular exposures are done. Size 1 film allows 4 maxillary and 3-4 mandibular exposures, suitable for individuals with strong gag reflex.

Suggested Posterior Exposure Sequence

  • Start with Quadrant 1 and move through Quadrants 2, 3, and 4, ensuring exposure begins with premolars then molars.

Special Cases in Film Placement

  • Shallow Palate: May require adjustment in technique (cotton rolls, increased vertical angulation).

Advantages and Disadvantages of the Paralleling Technique

Advantages

  • High accuracy with minimal dimensional distortion.

  • Simple and easy to learn.

  • Standardized method allowing for reproducibility.

Disadvantages

  • Challenging film placement, potentially uncomfortable due to film holders.

Additional Resources

  • Review material through recommended video resources.